First isolated in a lab in 2004, graphene has become the subject of an intense amount of scientific and industrial research seeking to capitalize on its unique and substantial optical and electrical properties. Graphene is formed of a monolayer of carbon atoms arranged in a hexagonal lattice. Graphene is highly flexible, yet has the strength hundreds of times that of steel and hardness of diamonds. Graphene is nearly transparent, but also efficiently conducts electricity and heat. Graphene exhibits ultrafast response over a broad spectral range along with significantly high nonlinearity.
Graphene's optical properties make it highly desirable for novel devices in the fields of optical wavelength converters, optical broadband polarizers, ultra short pulse generation, optical modulation, broadband nonlinear saturable absorbers in fiber lasers, and optical limiters. In addition, the fact that graphene exhibits both unique electrical and optical properties have opened the door for novel devices where the optical properties of the graphene are controlled through electrical signals.
Optical fibers are a key component of many of these novel graphene optical devices. When applied to optical fibers, graphene has been primarily applied to the optical fiber end face, or close to the optical fiber core along the length of the fiber in the direction of light propagation such as with D-shaped optical fibers or tapered fiber segments. When graphene is applied near the fiber core in the direction of light propagation, the light and graphene interaction occurs though an evanescent light field.
A variety of unique applications require the use of optical fibers that operate in the deep-ultraviolet (UV) spectrum. Deep-UV optical fibers are particularly useful for detection of proteins and drugs through fluorescence detection. Deep-UV optical fibers are also useful for laser delivery in medical procedures such as laser eye surgery. Deep-UV optical fibers also prove useful for bio-chemical analysis, UV spectroscopy, industrial chemical sensing, materials analysis and processing, lithography and UV laser marking/machining. In addition, deep-UV optical fibers hold promise for optical interconnect for electronic device communications between racked devices, communications between chips, and intra-chip communication. Increasingly, metal interconnect limits the performance of electronic devices as transistors continue to grow smaller. Replacing metal interconnect with optical interconnect would provide the improved power, latency, and bandwidth performance to match the enhanced scaling of transistors. Recently, researchers integrated 70 million transistors and 850 optical components into a silicon processor. While infrared light is common for optical fiber data transmission, choosing light with much lower wavelength, such as deep-UV, would facilitate the use of optical fibers with smaller diameters, thereby enabling miniaturization of the optical interconnect along with the advanced scaling of transistors. Two factors support the use of deep-UV optical fiber data transmission for optical interconnect: the development of deep-UV light-emitting diodes, and the development of UV fiber core materials resistant to UV-induced attenuation, otherwise known as solarization. When considering these optical fiber applications focused on the deep-UV spectrum, it is important to note that graphene exhibits an index of refraction lower than that of silica in the deep-UV spectrum. The question becomes is it possible to fabricate an optical fiber that includes a graphene layer as cladding for deep-UV applications.